1. Field of the Invention
The present invention relates to an elastic member employed in an ink passage of an ink-jet recording apparatus.
2. Description of the Related Art
Various ink-jet recording methods are known such as a thermal method and a piezo method. In the thermal method, a bubble is generated by means of rapid heating to eject ink from fine nozzles. In the piezo method, ink is ejected from fine nozzles by use of a piezoelectric element which deforms under impressing. The ink-jet recording method is a technology for forming an image by allowing a plurality of color inks of basic colors to selectively land on paper as fine droplets of several picoliters to several tens of picoliters.
The ink-jet recording method has advantages over other methods in that high text printing quality and high image printing quality can be obtained by controlling the ejection of the fine droplets. An image with sharp edges within image areas, no graininess and color reproduction close to full color can be formed by allowing the fine droplets of several picoliter volumes to land on paper from sufficiently fine nozzles with a high accuracy. In order to enable such an ejection of fine droplets, a high accuracy landing control technology is required. In order to facilitate this, it is necessary to prevent foreign materials interfering with the flow of ink from entering a portion in an ink-jet recording apparatus. This portion may be filled with ink, or may be a portion that comes into contact with the ink (hereinafter, each such portion is referred to as an ink passage). Therefore, several methods have been attempted to prevent the entry of the foreign materials into the ink passage. Specifically, for example, the assembly of the ink passage and the manufacturing of the ink are performed in a clean room, and ink is employed which is subjected to microfiltration through a filter having a pore size of less than 1 μm.
In an ink passage of an ink-jet recording apparatus, various elastic members are employed. For example, these elastic members may include: a cap which covers the nozzles of an ink-jet head; a wiper which cleans ink-jet head nozzle surfaces; a packing seal which is placed at the joint portion between components; a tube which supplies ink from an ink tank to the ink-jet head if the ink tank is provided separately from the ink-jet head; and the like. Generally, materials employed for constituting such elastic members are usually low cost and easily workable materials. Furthermore, additives such as a vulcanization agent and a vulcanization accelerator are added to these elastic members. When the elastic members come into contact with ink, these additives are dissolved out of the elastic members and precipitate in the ink passage. But it depends on the type of solvent used in the ink. Therefore, even when attempts are made to prevent the entry of foreign materials at the time of assembly of the ink passage and at the time of manufacture of the ink, the ink passage can only be maintained in a clean condition at an initial stage. In particular, if a temperature change or aging occurs within the ink passage filled with the ink or within the ink passage in contact with the ink, the additives tend to dissolve out of the elastic members employed in the ink passage and cause precipitation. The precipitations are formed not only in the ink before ejection from the nozzles, but also in ink adhering to the nozzle cap, the wiper or the like after ejection from the nozzles. Furthermore, the thus-formed precipitations may be supplied to the ink-jet head nozzles or to the periphery thereof through actions such as wiping or purging of the afore-mentioned nozzles. Precipitations in the nozzles or the periphery of the nozzles cause instability of the meniscus of the nozzles, the occurrence of clogging of the nozzles and a reduction in the water-repellency of the nozzle surface caused by flaws on the water-repellency film of the nozzle surface. Hence, the precipitations interfere with the high precision ink ejection, resulting in a reduction in image quality.
In view of such a problem, a method intended to overcome this has been proposed. In this method, rubber materials to be employed in an ink passage are immersed in water at 60° C. in a sealed container for a predetermined time to determine the amount of resultant dissolved materials, whereby a suitable rubber material is selected. In addition to this, another proposal has been put forward. In this proposal, the material to be employed to come into contact with ink would have an amount of fatty acid salts dissolved therefrom of less than or equal to a specific value when a sample piece of the material is immersed in the ink at 70° C. for 10 days.
However, even when a material selected using the method of either of the above-mentioned proposals is employed for an elastic member constituting an ink passage, a problem still exists in that the formation of precipitations in the ink passage cannot be prevented completely. This is because, since ink contains a high boiling point organic solvent and water, the appropriate selection of the elastic member is very difficult to make under the conditions in which an elastic material is simply immersed in water. Furthermore, precipitation components contained in an elastic member are not limited to the above-mentioned fatty acid salts. Components dissolved out of an elastic member into water or ink include a component which precipitates easily and a component which resists precipitation. Thus, even when the dissolved amount is simply measured, the measured value does not always correspond directly to the actual occurrence of precipitation.